World leaders are demanding an international investigation into the downing of Malaysian Airlines flight MH17 over eastern Ukraine, which killed all 298 people on board.

In a statement on Friday, the US President Barack Obama warned the "eyes of the world [are] on eastern Ukraine."

Calling for an immediate ceasefire in Ukraine, Obama demanded a credible investigation into the incident.

"We're going to make sure that truth gets out," he said, having called the crash a "terrible tragedy" on Thursday evening.

Prime Minister David Cameron described the air disaster as "absolutely appalling, shocking [and] horrific" and called for those responsible "to be held to account" after a chairing a meeting of the Government's Cobra emergency committee.

Mr Cameron is expected to speak to Russian President Vladimir Putin by telephone on Friday evening.

Prior to Mr Obama's statement on Friday afternoon, the United Nations (UN) Security Council backed a British-drafted statement calling for a "full, thorough and independent international investigation", during an emergency meeting preceded by a moment's silence for those killed in the crash.

The council members also stressed the need for "immediate access by investigators to the crash site to determine the cause of the incident."

At the meeting in New York, US Ambassador Samantha Power told delegates that Washington cannot rule out the possibility that Russia played some part in launching the surface-to-air missile that is believed to have shot down the Malaysian airlines jet.

She added that the US believes the plane was likely downed by an SA-11 missile fired from an area in eastern Ukraine controlled by pro-Russian separatists, which she alleged was provided by Russian among other heavy weapons - charges which Moscow denies.

Ms Power added that due to the "technical complexity" of the device, it is unlikely separatists could have operated it with assistance.

"Thus, we cannot rule out technical assistance from Russian personnel in operating the systems," she said, adding: "it is extremely important that an investigation be commenced immediately."

At the meeting called by Britain, UK's ambassador Sir Mark Lyall Grant said "searching questions" had to be asked about Russia's links with armed separatists and called for Moscow to issue an "unequivocal condemnation" of their actions. He went on to urge Russia to "reflect carefully on the situation they have created" by allegedly support armed separatist groups.

Russian UN Ambassador Vitaly Churkin addresses an emergency UN Security Council meeting (AP)Russia's UN ambassador responded by warning the council against making "broad statements and insinuations" regarding the cause of the crash.

"There is a need for impartial, open investigation of what happened. Pressure should not be brought on this investigation, trying to prejudge its outcome with broad statements and insinuations that are unjustified in such a difficult situation," Ambassador Vitaly Churkin said.

Churkin also questioned why Ukrainian aviation authorities allowed a passenger flight through an area of armed clashes where anti-aircraft systems were working, adding that ensuring the security of civilian aviation in a state's airspace is the that state's responsibility.

Earlier on Friday, White House spokesman Josh Earnest said it "is critical that there be a full, credible, and unimpeded international investigation as quickly as possible". He told a news conference it was "vital that no evidence be tampered with in any way and that all potential evidence and remains at the crash site are undisturbed".

Pro-Russian separatists have since told the Organization for Security and Co-operation in Europe (OSCE), a security and rights body, they would ensure safe access for international experts visiting the scene.

German Chancellor Angela Merkel echoed the call for an independent investigation into the crash to be started as quickly as possible, telling a news conference in Berlin: "There are many indications that the plane was shot down, so we have to take things very seriously.

"These events have once again shown us that what is required is a political solution and above all that it is also Russia that is responsible for what is happening in Ukraine at the moment," she added.

The Ukrainian Prime Minister Arseniy Yatsenyuk described the downing of the plane as an "international crime" and a "war against the world" as he called for an emergency meeting of the UN Security Council. "All lines have been crossed," he added.

Video: If deliberate, 'those responsible must be held to account'

Responding to the crash, Mr Putin demanded a "thorough and unbiased" investigation into the incident during a phone call with Dutch Prime Minister Mark Rutte, the Kremlin said on Friday.

Later, he called for a ceasefire by pro-Russian separatists and Ukrainian government forces fighting in eastern Ukraine to allow for negotiations during a meeting with Russian Orthodox Church leaders.

"All sides in the conflict must swiftly halt fighting and begin peace negotiations," he said. "It is with great concern and sadness that we are watching what is happening in eastern Ukraine. It's awful, it's a tragedy."

In a television interview, the former US Secretary of State Hillary Clinton suggested the plane could have been shot by Russian-backed separatists, and said action was needed to "put [Vladimir] Putin on notice that he has gone too far and we are not going to stand idly by".

She told PBS news: “There does seem to be some growing awareness that it probably had to be Russian insurgents. How we determine that will require some forensics, but then if there is evidence pointing in that direction, the equipment had to have come from Russia. What more the Russians may or may not have done, we don't know.”

US senator John McCain also warned that there will be “hell to pay” if the Russian military or separatists are deemed to have had any involvement in the 'incident'.

It comes as video footage has emerged purported to show a tank driving through Ukraine which reports claim could be a BUK missile launcher.

The video allegedly show a BUK launcher being driven into place, The Evening Standard has reported. US and Ukrainian officials have said they believe the plane was shot down by a missile.

The authenticity of the video has not been in anyway confirmed or verified.

Leaders of the rebels' self-proclaimed Donetsk People's Republic denied any involvement and said a Ukrainian air force jet had brought down the intercontinental flight.

The Ukrainian government has this morning released recordings it said were of Russian intelligence officers discussing the shooting down of a civilian airliner by rebels who may have mistaken it for a Ukrainian military plane. These have also not been confirmed or verified.